The present invention relates generally to the field of orthodontics.
One objective in orthodontics is to move a patient's teeth to a position where the teeth function optimally and are also aesthetically pleasing. Conventional appliances such as braces and wires can be positioned on a patient's teeth by a treatment provider such as an orthodontist or a suitably trained dentist. Once mounted on the teeth, the hardware exerts continual forces on the teeth and gradually urges the teeth toward their ideal positions. Over a period of time, the treatment provider adjusts the braces and the wires to move the teeth toward their final destination.
Orthodontic brackets are often bonded directly to the patient's teeth. Typically, a small quantity of adhesive is placed on the base of each bracket and the bracket is then placed on a selected tooth. Before the adhesive is set, the bracket is maneuvered to a desired location on the tooth. Once the adhesive has hardened, the bracket is bonded to the tooth with sufficient strength to withstand subsequent orthodontic forces as treatment progresses. One shortcoming with this technique is the difficulty in accessing the optimal surface for bracket placement on severely crowded teeth or in teeth where the bonding surface is obstructed by teeth in the opposing arch during jaw closure. With posterior teeth, the treatment provider may have difficulty seeing the precise position of the bracket relative to the tooth surface. The amount of time needed to carry out the bonding procedure may be a nuisance both to the patient as well as to the treatment provider. Also, the necessity of minimizing moisture contamination from the patient's saliva can prolong the procedure and also unduly impair the accuracy of placement of the brackets on the teeth. All of these factors increase the chance that the ultimate adhesive bond will not have sufficient strength to retain the brackets on the teeth during treatment. One way to overcome some of the limitations of direct bracket placement is with indirect bonding. Typically, an impression of each of the patient's dental arches is taken and a replica plaster or “stone” model is made from each impression and sealed. Brackets are bonded to the sealed stone models using a temporary cement. A transfer tray is then made by placing matrix material over both the model and the brackets on the model. For example, a heated plastic sheet matrix material may be placed over the model and brackets and then under pressure. The plastic sheet material then assumes a configuration that precisely matches the shape of the replica teeth of the stone model with the brackets in the desired position. The plastic material is then allowed to cool and harden to form a tray. The temporary adhesive is removed, permanent adhesive is placed on the base of each bracket in the tray, and the tray with the embedded brackets then placed over matching portions of the patient's dental arches. Since the configuration of the interior surface of the tray closely matches the respective portions of the patient's dental arches, each bracket is ultimately positioned on the patient's teeth at precisely the same location that corresponds to the previous location of the same bracket on the stone model. The adhesive is hardened and the matrix material removed, leaving the brackets in the desired positions. This method however, is labor intensive. An additional problem with the indirect method is that brackets may become dislodged during the removal of the matrix from the dental arches. The problem of proper access to tooth surfaces for optimal placement in the event of severely crooked teeth or teeth which interfere with the opposing arch such that brackets cannot be placed is also not addressed.
New methods such as those described in U.S. Pat. No. 5,975,893, commonly assigned to the assignee of the instant invention, allow the treatment to be planned in advance and a plurality of polymeric shell appliances are fabricated at the outset of treatment. The use of polymeric shell appliances provides treatments that are more comfortable; less visible, and removable by the patient, and greatly improves patient compliance, comfort, and satisfaction.
Since each patient is unique and requires customized treatment, on occasion, a patient may need to utilize a combination of braces/wires and shell appliances. Ideally, a device would enable precise placement of brackets on teeth with minimal risk of displacing the brackets upon removal of the matrix and allow final placement to be independent of adjacent geometries. In other words, placement of obscured tooth surfaces may be accomplished at a later time when the tooth surfaces have been exposed through initial uncrowding of severely overlapped teeth.